1. The Field of the Invention
The present invention relates to organically complexed nanocatalysts for use in improving the combustion properties of fuels. The present invention also relates to modified fuels that incorporate such organically complexed nanocatalysts, as well as methods for manufacturing such nanocatalysts and fuel compositions incorporating such catalysts.
2. Related Technology
Carbon-containing fuels typically combust to yield mainly carbon dioxide and water as the major products of combustion. Due to incomplete combustion, however, other more harmful molecules can be formed, such as carbon monoxide (CO), hydrocarbons and soot. Impurities in the fuel can also yield significant quantities of ash, SOx and NOx. Due to increased environmental awareness and stricter governmental guidelines, there are ongoing efforts to reduce the release of harmful emissions into the environment.
Coal combustion is major source of energy for the production of electricity throughout the world. Coal is a good source of energy because of its high energy to weight ratio and its great abundance. The use of coal, however, is increasingly under scrutiny because of environmental concerns. Among the known environmental difficulties with coal combustion is the production and emission of NOx compounds, such as NO, N2O, and NO2. NOx compounds can be very harmful to human health and are known to produce undesirable environmental effects such as smog.
Government regulations require emission from coal burning to be monitored and controlled. Controlling NOx emissions has become increasingly difficult as government regulations continue to lower the allowable level of NOx and other pollutants that can be released into the environment. The requirement for reduced pollutants from coal-fired power plants has led to a demand for suitable new technologies.
In a coal fired power plant, there are two principle sources of NOx formation: fuel NOx and thermal NOx. Fuel NOx is NOx that forms from nitrogen found in the fuel, whereas thermal NOx is formed from other sources of nitrogen such as nitrogen in the air. About 80% of NOx emissions from coal combustion are produced from fuel nitrogen.
One method used to reduce pollutants during coal combustion focuses on removing NOx from power plant flue gas. For example, NOx emitted in flue gas can be removed using selective catalytic reduction (SCR), which converts NOx compounds to nitrogen gas (N2) and water. However, this type of NOx control method is expensive, in part, because of the required capital investment. The cost of these technologies and increasingly stringent government regulations have created a need for less expensive technologies to reduce NOx emissions from coal combustion.
Another method of reducing NOx emissions is to remove coal nitrogen from the coal material by converting it to N2. Recently, researchers have discovered that iron-based catalysts can assist in releasing fuel nitrogen from coal. In work by Ohtsuka and coworkers at Tohoku University (Sendai, Japan), methods have been described for the production of an iron-based catalyst, which, when combined with coal and placed in an pyrolysis environment, causes nitrogen compounds in coal to be released more rapidly, thus causing a decrease in the amount of nitrogen remaining in the char material (Ohtsuka et al., Energy and Fuels 7 (1993) 1095 and Ohtsuka et al., Energy and Fuels 12 (1998) 1356).
Several features of the catalyst and methods used by Ohtsuka make Ohtsuka's catalyst and methods too expensive and less effective than desired for use in coal fired power plants. First, Ohtsuka teaches precipitating a FeCl3 solution directly onto the coal using Ca(OH)2. Precipitating the catalyst onto the coal results in intimate contact between the coal and the catalyst precursors and other reagents used to make the catalyst nanoparticles. While Ohtsuka suggests washing the coal to remove chloride and calcium, this step requires washing the entire coal feedstream, which would be very costly on an industrial scale. Furthermore, at least some of these chemicals are likely to be adsorbed by the coal and remain even after washing. Introducing compounds such as chloride and calcium can have an adverse effect on power plant equipment and can cause pollution themselves.
In addition, precipitating the catalyst onto the coal requires that the catalyst be formed in the same location as the coal. This limitation could require that the catalyst be prepared at a coal mine or power plant, or that the coal material be shipped to a separate facility for catalyst preparation, thereby adding to production costs.
Another disadvantage of Ohtsuka's catalyst is that it requires high loading amounts to obtain desired results (e.g., up to 7% by weight of iron). High loading amounts can increase costs and offset the benefits of using a relatively inexpensive material such as iron. In addition, high iron content contributes to ash formation and/or can alter the ash composition.
Other solid fuels that emit pollutants into the environment include charcoal, wood and biomass, commonly due to incomplete combustion. Typical pollutants from these fuels include CO and hydrocarbons. Another substance that is a solid “fuel” is tobacco, which is deliberately combusted in a way so as to yield smoke that is inhaled or puffed into the body. In addition to desired large molecules, such as nicotine, tobacco combustion produces undesired small molecules such as CO and nitric oxide (NO). More information related to tobacco and efforts to reduce the formation of undesired small molecules are set forth in copending U.S. application Ser. No. 11/054,196, filed Feb. 9, 2005, which was previously incorporated by reference.
What is needed are improved catalysts that can be applied to or combined with solid fuels, such as coal, charcoal, wood, biomass, tobacco, or fuel oils to reduce undesired pollutants during combustion.